Building on our Phase I achievements, we will design and deploy a handheld, breath-based medication adherence monitoring system (adherence system) to identify adherence for clinical trials. The system consists of a miniature, battery powered gas chromatograph (the device) capable of measuring volatile metabolites (e.g., butanone) on an individual's breath after ingestion of a medication containing taggants (e.g., 2-butanol). This data can be sent to and evaluated by health care personnel via HIPAA-compliant information technology to allow opportunity to improve medication adherence. In Phase II activities, we propose a plan to optimize the design of the adherence system. The proposal consists of 7 aims. Specific Aim 1: Chemistry - characterize "generally recognized as safe" taggants for definitive adherence in humans. a) Determine breath pharmacokinetic parameters of two definitive taggants and their key volatile metabolites in fasting humans (months 1-6), and b) create a chemistry backup program to develop new definitive taggants (months 1-24). [Specific Aim 2: Food Interference - further validate that food does not interfere with this adherence system (months 6-12)]. Note: new aims are bracketed and in Georgia font. Specific Aim 3: Pharmacy - optimize the means whereby taggants are interfaced to pharmaceutical products for definitive adherence (months 1-24). Specific Aim 4: Portable Gas Sensor - finalize design of the mGC-MOS, a) optimize mGC and MOS components of mGC-MOS unit, b) design, implement and optimize a breath collection device, and c) identify a contract manufacturer (months 1-12). [Specific Aim 5: Information Technology and Data Processing - develop methods and techniques to locally store, transmit, remotely archive, and distribute adherence data in a HIPAA-compliant manner. Develop signal processing algorithms to improve taggant detection accuracy of device. (months 1-12) Specific Aim 6: Adherence System Accuracy - Conduct a pilot study in humans to test system performance (months 12-18). Specific Aim 7: Behavioral (Usability) Adherence System Evaluation - Conduct a pilot study in high risk, HIV/AIDS patients to test acceptance of the system (months 18-24).] The ability to stratify medication adherence rates to safety and efficacy parameters and linking adverse events to medication ingestion will lead to optimal decisions regarding clinical trial drugs safety and efficacy. PUBLIC HEALTH RELEVANCE: Nonadherence to prescribed medication regimens is a major health issue in the US which costs our healthcare system over $100 billion annually. Nonadherence is a major cause of morbidity and mortality. It can result in a public health threat if, for instance, a patient fails to adhere to an antibiotic or antiviral medication. This can lead to the emergence of resistant organisms. We propose to develop a small portable device that a patient can blow into shortly after taking their medication which will detect and document that the appropriate medication was taken at the proper time. This technology should improve adherence rates, especially in high-risk populations, and provide pharmaceutical companies and the FDA with an improved data set for evaluating drugs in clinical trials.